block http access to all folders

This folder should never be publicly accessible. Its contents should
ever ONLY be requested through PHP includes or requires. The
functions.*.php aren't really "bad" to be accessible publicly as
everything is encapsulated in functions; however, swiftmailer is not and
comes with test files and such that could do something nasty if
swiftmailer commited something malicious. I know, extremely unlikely,
but my paranoia gets the best of me.